Currently, legacy telephony systems and Session Initiation Protocol (SIP) systems are intermixed on various networks. To further complicate the matter, SIP networks may have a mix of basic SIP devices (RFC 3261) and advanced SIP devices (RFC 4235, draft-mahy-sip-remote-cc). In a mixed-environment, existing systems are able to monitor a specific endpoint and are able to detect events associated with the specific endpoint However, existing systems are unable to monitor events using a single API call on one or more additional devices where there is a call between the specific endpoint and the second device if the endpoint and the device are not the same type of devices (either legacy, SIP basic, or SIP advanced). The second device cannot be tracked because legacy, SIP basic, and the SIP advanced systems use different call identifiers.
For example, Patent Application Publication 2007/0143858 describes a system for monitoring events associated with individual SIP devices. A programming interface can be used to monitor a specific SIP device for specific events associated with the device. As calls are made either to or from the monitored SIP device, the system can detect events on the other SIP device as long as the monitored SIP device and the other SIP device are both SIP basic devices. If the call is to/from a legacy device or a SIP advanced device, the system cannot detect events happening to the other device because the call information does not flow through the Signal Path Manager.